1. Field of Invention
This invention relates to antifreeze compositions and more particularly to such compositions suitable for use as coolants in internal combustion engines.
2. Description of the Prior Art
The ethylene glycol and similar polyhydric alcohol antifreeze solutions containing various corrosion inhibitors which are on the market today meet practically all of the requirements of a permanent coolant for internal combustion engines. Use of corrosion inhibitors has extended the useful life of the antifreeze solutions from one year to two years before being drained out of the engines cooling systems.
Corrosion inhibitors described in the art include sodium tetraborate (Kepfer, U.S. Pat. No. 1,911,195); sodium tetraborate with mercaptobenzothiazole (Keller, U.S. Pat. No. 2,373,570); and alkali metal tetraborate with an alkali metal phosphate (Kiffer, U.S. Pat. No. 2,384,553); and an alkali metal meta borate (Cutlip and Scheer, U.S. Pat. Nos. 2,937,145 and 2,937,146). Even though these compositions are adequate, a glycol-water concentration indicator has been discussed as a desirable feature for use in internal combustion engine coolants to control freezing point detection.
Some concepts which were thought to be suitable but which proved to be ineffective were indicators based on the phenomena of solvatochromism, hydrogen bonding and pH. Solvatochromism refers to the effect exhibited by some classes of dyes which change their color with changing solvents. In general, the color change exhibited is more satisfactory when solvents are of widely differing chemical nature such as aromatic hydrocarbons and ketones. With a solvent pair such as water and ethylene glycol, large color changes would not be expected to be encountered. In fact, two dyes, known to exhibit the effect, i.e., phenol blue and Quinoline yellow are ineffective.
The hydrogen bonding effect and pH effect are not suitable and effective means for indicating a shift in the water-glycol make-up.